1. Field of the Invention
The present invention relates to quartz oscillators used for oscillating devices including a quartz thin-film vibrator, and particularly relates to a quartz oscillator including a quartz filter and to a method for manufacturing the quartz oscillator.
2. Description of the Related Art
A quartz oscillator is generally referred to as one having a quartz blank designed on the basis of the required performance, thin-film electrodes provided on the surfaces of the quartz blank, and a retainer including a thin supporting plate functioning as both mechanical support and an electrical lead, wherein the quartz blank and the thin-film electrodes are stored in the retainer in a sealed manner. On the other hand, a quartz filter is a device having a function of extracting required frequency components from various signal components and attenuating undesired frequency components. Among such filters, an MCF (Monolithic Crystal Filter), which includes two electrodes provided on a crystalline wafer and which has filter characteristics based on a combination of two vibration modes, is widely known. Since the present invention generally relates to quartz oscillators, structures thereof, and manufacturing methods thereof, the term quartz oscillator includes quartz filters and is used in a broad sense herein.
Quartz oscillators are used as important devices essential to information communication because of their high stability. Recently, with the development of communication satellites and mobile phones, high performance and miniaturization have been strongly required.
Depending on the above requirements, various methods have been proposed. A method for manufacturing a monocrystalline quartz thin-film by a sol-gel process is disclosed in Japanese Unexamined Patent Application Publication No. 8-157297, and a method for processing a quartz blank is disclosed in Japanese Unexamined Patent Application Publication No. 5-327383. In Japanese Patent Application No. 2000-270300, the inventors have proposed an atmospheric pressure vapor phase epitaxy (AP-VPE) method in which epitaxial growth is performed on a base by the reaction of silicon alkoxide with oxygen in atmospheric pressure without using a vacuum apparatus.
Since the frequencies used in mobile communication systems have reached the GHz band, the quartz oscillators used therein should generate higher frequencies.
Since the oscillating frequency of a quartz oscillator is inversely proportional to the thickness of the quartz blank, the quartz blank should have a small thickness. However, it is difficult to achieve a quartz blank having a thickness of 40 μm or less by current processing methods. Thus, the oscillating frequency of mass-produced quartz oscillators has not exceeded about 40 MHz when using the fundamental wave.
In order to increase the frequency, it is necessary to employ a processing method such as wet etching or dry etching. However, when the etching rate is reduced to improve the control of the thickness, there is a problem in that it takes a long time to achieve a desired thickness because the large quantity of quartz chippings formed by etching needs to be removed.
In order to solve the above problem, the inventors have developed an atmospheric pressure vapor phase epitaxy (AP-VPE) method in which epitaxial growth is performed on a base by the reaction of silicon alkoxide with oxygen in atmospheric pressure without using a vacuum apparatus, and have made a patent application, filed as Japanese Patent Application No. 2000-270300.